However some descriptions make peltasts seem to be much more heavily armed and protected than this - such as vases showing armoured hoplites carrying a pelte. In addition, Xenephon describes the peltats that engaged the Persian cavalry as being armed with swords as well as javelins. Field of Glory army lists provide for these types of 'super-peltasts'.
Thracian peltasts had a sling (baldric) on their pelte which meant they could carry their shields on their backs as they evaded the enemy (providing the opportunity to both run faster and have a modicum of protection as they did so, one presumes).
This style of fighting - for the Greeks at least - originated in Thrace and Thracian peltasts were sought after for their skirmishing ability. Peltasts really came into their own during the Pelopennesian War as the Athenians sought ways of combatting Sparta's superiority in hoplite warfare.
Peltasts became the mainstay of Greek armies in the 4th century BC (as they were cheaper to recruit and maintain than heavily armoured hoplites). At the battle of Lechaeum, General Iphicrates used mainly peltasts to destroy a Spartan hoplite phalanx. However, an account of this battle suggests that Iphicrates provided his peltasts with long spears rather than javelins (again, creating a different idea of what a peltast was).
If so, these lighter armed soldiers armed with a long thrusting spear may well have been the precursor to the Macedonian pikeman (who also had a small shield slung over the shoulder) - though there is some evidence that some peltasts simply preferred a thrusting spear to a javelin.
Certainly Alexander relied heavily on Thracian peltasts but these were gradually replaced by theurophoroi. References to peltasts after the 3rd Century BC is considered to refer to 'mercenary' rather than skirmishing troops - again explaining why some references to peltasts in the Field of Glory rules show them as heavily armed swordsmen rather than light javelin troops.
Peltasts were certainly not the sole preserve of Greek armies. The Persian deployed similar troops from the 5th Century BC onwards, similarly equipped but carrying an axe as a sidearm. These were known as takabara (the shield being the 'taka').
In the Antigonid armies of Macedon, there was an elite corps of peltasts (which included the Agema) numbering between 3,000 and 5,000 - but it is suggested that these were not typical skirmishers but protected spearmen which operated in a phalanx ('pelte' simply describing a typical Macedonian shield)
Deployment
The typical peltast was used as flank protection - acting as a link between the main line and the cavalry (especially on broken ground). Otherwise they were used in support of other skirmish troops.
But they had other uses. Xenephon mentions how the Persian cavalry charged the peltasts, who parted to let the cavalry through without incurring any casualties and then closing ranks to engage the cavalry from the rear. This would be tricky to replicate in Field of Glory however!
If facing hoplites (or similar) they would loose their javelins at close range (to kill and injure and therefore disrupt the battle line) then evade. As they were more lightly armoured and carried less equipment, they could usually get away if pursued - and offered the additional advantage of breaking up the battle line by doing so. The power of the phalanx was in its cohesion - it mattered more about keeping a tight line of shields than individual prowess with spear or sword. So if hoplites charged peltasts and then met the opposing (unbroken) line of a hoplite phalanx, they were likely to lose the battle.
Indeed, peltasts would often charge, evade and then exploit the gaps left when pursued (especially over difficult ground).
In terms of other descriptions of what a peltast actually was, it depends on what the troop type actually was - and as seen above, the descriptions are wide and varied.